Device for thermally treating substrates

ABSTRACT

The aim of the invention is to enable substrates to be thermally treated in a more homogeneous manner. In order to achieve this, a device is provided for thermally treating substrates, especially semiconductor wafers, comprising at least two adjacent, essentially parallel heating elements which respectively have at least one heating wire. The two adjacent heating elements are embodied in such a way that they are quasi-complementary, at least in parts, in terms of the coiled and uncoiled segments of the heating wires pertaining thereto.

[0001] The present invention relates to an apparatus for the thermaltreatment of substrates, especially semiconductor wafers, with at leasttwo adjacent heating elements that are disposed essentially parallel toone another and are each provided with a heating filament. The apparatusis in particular related to a rapid heating unit in which the substratesare subjected to rapid temperature changes.

[0002] In the semiconductor industry, it is known to thermally treatwafers during the process of manufacturing the same. For this purpose,generally so-called rapid heating units are utilized, such as aredescribed, for example, in DE-A-19952017, which originates from the sameapplicant. These units include a reactor having lamps for heating thesubstrates (preferably only one substrate is disposed within thereactor), and generally, although not necessarily, a process chamber(preferably of quartz glass) that is transparent for the lamp radiationand that is disposed within the reactor and surrounds the substrate. Thesubstrate is subjected via the lamp radiation within the reactor or theprocess chamber to a thermal treatment pursuant to a predefinedtemperature-time-curve in a defined process gas atmosphere or in avacuum. For the process result of the thermal treatment, it is veryimportant that the wafer be heated uniformly, and that a homogeneoustemperature distribution result on the wafer surface, or that apredefined temperature distribution can be realized as well as possible.Deviations from a homogeneous temperature distribution over thesubstrate are especially advantageous for silicon wafers if the processtemperatures exceed 1200° C. and the heating and cooling rates aregreater than 50° C./s. Under these process conditions, it has been shownthat in the region of the final temperature an approximately parabolictemperature distribution having a temperature difference of about 5 to20° C. (as a function of the diameter of the wafer) over the waferdiameter provides the best process results with regard to freedom ofslip. However, such uses with desired, defined non-homogeneoustemperature distribution over the wafer or the substrate are more theexception, since these processes entail the greatest demands on theregulatability and the temperature measurement of the substratetemperature, which only the most modern plants today can fulfill.

[0003] Primarily during the heating and cooling phases, there occurswith disc-shaped wafers the problem of very non-homogeneous temperaturedistributions, especially in the edge region of the wafer, which cannotbe controlled or can be controlled only inadequately. Thus, the edge ofthe wafer heats much more significantly and rapidly during the heatingphase than does the inner portion of the wafer. This more rapidheating-up is due to the fact that at the edge of the wafer, a largerouter surface per volume of wafer is provided than in the interior ofthe wafer. Via this additional outer surface, the edge of the waferabsorbs more of the heat radiation than does the interior of the wafer(edge effect). Furthermore, the edge of the wafer is irradiated by alarger wall surface of the reactor, essentially via reflection ofradiation, and “shadows” the interior of the wafer. Due to the reactorwalls, the edge region of the wafer is thus irradiated that much moreintensely the higher is the reflectivity of the wall surfaces. Thus,during heating-up of the wafer, the edge of the wafer, in addition tothe pure “edge effect”, is additionally heated due to the presence ofthe reactor walls. Since the reactor walls of rapid heating units areusually cooled (cold wall reactors), and the wall temperature isgenerally less than 100° C., the reactor walls have a relatively lowthermal inherent or characteristic radiation relative to the reflectedradiation, as a result of which the influence thereof during usualprocess temperatures of greater than 400° C. can be disregarded.

[0004] On the other hand, during the cooling phases the wafer cools morerapidly at the edge of the wafer than in the interior of the wafer,since via the larger surface per wafer volume at the edge, more thermalradiation is emitted. In addition, surfaces of the reactor chamber thatare disposed across from the substrate and are generally arrangedparallel to the substrate reflect the radiation energy given off fromthe wafer back to the center of the wafer in a reinforced manner,thereby further slowing down the already slow cooling-off of the centerof the wafer. This slowing down is that much greater the more reflectiveare the surfaces, or the more these surfaces radiate thermal energy. Theinfluence of the edge of the wafer and of the process chamber walls uponthe homogeneity of the temperature is also designated as thephoton-box-effect, and is, among other things, essentially a result ofthe reflection of a portion of the heat radiation at the reflectivechamber walls, and is included in the main problems during the rapidheating of semiconductor substrates, especially if during the entireduration of the process, in other words also during the dynamic phasesof the heating-up and cooling-off, an as uniform as possible or apredefined temperature distribution (which itself can again be afunction of the temperature) is to be achieved over the wafer.

[0005] From the aforementioned DE-A-19952017 it is known to surround thewafer with a compensation ring in order to reduce the photon-box-effect.In particular, the compensation ring is tilted as a function of theprogress of the process in order to achieve a shadow effect relative tothe lamps at the edge of the wafer. In addition to this approach, it isalso known to provide light-transforming plates, also knows ashot-liners, parallel to the wafer in order to indirectly heat the wafervia such plates, and hence to reduce the photon-box-effect. However,these approaches can only partially reduce the photon-box-effect, andthey lead to a complicated construction of the rapid heating unit.

[0006] In the known rapid heating units, rod-shaped tungsten-halogenheating lamps are generally utilized. The heating lamps are providedwith a tungsten filament that is kept in a halogen-containingatmosphere. During the operation of the lamps, tungsten from thefilament is volatilized and reacts with gas molecules to form tungstenhalide. During the operation of the lamps below approximately 250° C., acondensation of the tungsten on the lamp tubes can occur, which,however, can be avoided if the lamp glass is kept in a temperature rangebetween 250° C. and 1400° C. The condensation should be avoided, since afog connected therewith on the glass adversely affects the heatingprocess and the service life of the lamps. If the tungsten halide comesinto the vicinity of the filament, sufficient thermal energy is appliedto break the chemical bond and to again deposit the tungsten upon thefilament. Subsequently, the halogen gas can repeat the process. Thiscycle is known as the halogen process.

[0007] With the conventional rod-shaped tungsten-halogen lamps, thefilament extends approximately in the center of the lamp cross-sectionalong the longitudinal axis of the lamp, and is uniformly spirallycoiled essentially over the entire length of the lamp. Only in the endregions are linear filament sections provided for the transition intothe respective lamp socket. As a result, an essentially uniform heatingcapacity can be achieved over the entire length of the lamp, which,however, contributes to the aforementioned photon-box-effect since, asmentioned above, with a uniform heating capacity over the surface of thewafer the edge region is heated more pronounced than is the centralregion.

[0008] With the aforementioned DE-A-19952017 the wafer that is to betreated is furthermore disposed in a process chamber that comprisesquartz glass, whereby the heating lamps are disposed outside of theprocess chamber. The quartz glass is transparent for the radiationemitted from the heating lamps. After a heating of the wafer within theprocess chamber, the wafer emits a short wave thermal radiation in therange of 0.3 to 4 μm, as well as a longer wave thermal radiation in theinfrared range of greater than 4 μm. The quartz glass of the processchamber is not entirely transparent for this longer wave thermalradiation of greater than 4 μm, and therefore a large portion of thisthermal radiation is absorbed by the quartz glass. Thermal radiationthat is not absorbed is reflected back to the chamber, and again a largeportion is absorbed in the quartz glass. A remainder falls on the waferand is absorbed thereby. Due to the absorption of the thermal radiationin the quartz glass, there is a localized heating-up of the processchamber, especially in a region of the process chamber that is disposeddirectly above or below the wafer. This effect is further reinforced bya reflection of the thermal radiation at the reflective chamber walls ofthe unit, since the thermal radiation is essentially reflected directlyback to the wafer, so that a region of the process chamber thatessentially corresponds to the projected shape (i.e. having the samecircumferential shape) of the substrate is heated significantly morethan regions disposed beyond this region. This process again reinforcesthe so-called photon-box-effect, especially if the process chamber isgreatly heated up, so that it irradiates back to the wafer within thechamber. This return radiation prevents a rapid cooling of the wafer,especially in the middle of the wafer. The process chamber of quartzacts as a sort of energy trap for the long wave thermal radiation,whereby due to a coupling between wafer and process chamber the centralregion of the wafer is always irradiated more strongly, since theprocess chamber walls that are disposed approximately across from thisregion are at a higher temperature than are the other process chamberwalls. This makes it clear that a non-homogeneous temperaturedistribution of the process chamber (e.g. of quartz) has an influenceupon the temperature distribution of the wafer. For this reason, it isattempted to cool the process chamber as homogeneously as possible.However, the process chamber temperatures can readily reach a range of600° C.

[0009] Proceeding from the aforementioned state of the art, the objectof the present invention is to provide an apparatus for the thermaltreatment of substrates, especially semiconductor wafers, that enables amore homogeneous or defined heating of the substrate that is to betreated.

[0010] Pursuant to the present invention, this object is realized withan apparatus for the thermal treatment of substrates, especiallysemiconductor wafers, having at least two adjacent heating elements thatare disposed essentially parallel to one another and are each providedwith a heating filament, wherein the two adjacent heating elements, atleast in part, are embodied approximately complementary to one anotherwith respect to the coiled and uncoiled sections of their heatingfilament.

[0011] The complementary configuration of the heating filaments of thetwo adjacent heating elements means that at least one coiled section ofthe filament of a heating element is disposed entirely or at leastpartially in the region of an uncoiled section of the heating filamentof the adjacent heating element. Conversely, an uncoiled section of theheating filament of a heating element can be disposed entirely or atleast partially in the region of a coiled section of the heatingfilament of the adjacent heating element.

[0012] By providing uncoiled and coiled sections of at least twoadjacent heating elements that are disposed approximately parallel toone another, whereby the sections are embodied approximatelycomplementary to one another, it is possible to achieve over the surfaceof the wafer, especially along the filaments, differently controllableradiation intensities, which can be used to reduce thephoton-box-effect. The irradiation characteristics of the filaments ofthe at least two heating elements can be adapted to the temperatureconditions that exist in or on the wafer by appropriate activation withelectrical power. Mechanical additional elements, such as, for example,a compensation ring or a hot-liner, for reducing the photon-box-effect,can be eliminated.

[0013] The present invention advantageously offers the possibility, withan appropriate arrangement of the adjacent heating elements, for thelatter to heat the wafer in such a way as if it was being irradiatedfrom a single heating element, i.e. as if only a single heating filamentwere present that, however, due to the approximately complementarysections is controllable with respect to its irradiation intensity ifthe individual heating elements are individually electrically activated.This considerably broadens the ability to regulate in comparison toprevious rapid heating units having rod-shaped lamps without having toreduce the previous power features of the units, since the units can atany time be operated in such a way as if they were equipped withconventional rod lamps.

[0014] The filament of a heating element preferably has n coiledsections and m uncoiled sections, whereas the filament of the adjacentheating element has m coiled and n uncoiled sections, whereby n and mare respectively integers. This enables a complimentary arrangement ofcoiled and uncoiled sections of adjacent heating elements. The coiledsections of the one filament of a heating element are preferablyrespectively disposed at least partially in the region of the uncoiledsections of the filament of the adjacent heating element. In so doing,the coiled sections of the filaments can overlap at most 30% of theirsectional length or 10% of the diameter of the substrate that is to betreated. In the same manner, the uncoiled sections of filamentspreferably overlap at most 10% of the diameter of the substrate that isto be treated. One embodiment of the invention can also have nooverlapping of the correspondingly complimentarily embodied sections.The degree of overlap depends upon how close to one another thefilaments that are complimentarily embodied relative to one another are,and what requirements are prescribed relative to the permissibledeviations of the desired temperature distribution upon the wafer.

[0015] Pursuant to a preferred embodiment of the invention, thefilaments are symmetrical relative to a plane of symmetry that centrallyintersects the longitudinal axis of the filaments and is perpendicularthereto, with this being done to obtain a symmetry that is adapted tothe substrate. Preferably, respectively at least two adjacent inventiveheating elements are associated with one another on at least one sideand form a group. In this connection, the heating elements of a groupare preferably provided with a common socket in order to hold thegrouped heating elements in a defined position relative to one another.The heating elements of a group can advantageously be individuallyelectrically activated in order in this manner to be able to control thespatial irradiation profile along the axis of the heating elements ofthe group. Furthermore, the individual groups can similarly beindividually electrically activated in order to be able to also controlthe irradiation profile of the groups in the direction of the extensionof the groups. The groups are advantageously disposed approximatelyparallel to one another and parallel to a plane that is advantageously asurface of the wafer. By appropriate activation of the groups and theheating elements within a group, the possibility is provided, not onlyin the longitudinal direction of the heating elements but also in thedirection perpendicular thereto, of controlling or regulating theintensity of the irradiated power. In this way, it is possible togenerate different irradiation profiles over the surface of thesubstrate. The respective filaments advantageously have a constantelectrical resistance per unit of length in order over the length of thecoiled section of the filament to produce a constant irradiationintensity. Deviations herefrom can also be advantageous, especially thedensity and/or type of coiling of the coiled sections can benon-homogeneous.

[0016] At least one heating element advantageously has at least twochambers for accommodating the filament, and in particular a pluralityof chambers that are separated from one another for accommodatingdifferent sections of the filaments. By providing different chambers,the halogen process can be optimally established in the respectivechambers, especially taking into consideration the respective filamentsection. Especially in the region of the uncoiled sections of thefilaments there exists the danger of condensation of the tungsten on thelamp tube, since in the region of the uncoiled sections there is alesser heating than in the region of the coiled sections. For a goodcontrol of the halogen process as a function of the different sections,a different pressure and/or a different gas is provided in at least twoof the chambers.

[0017] To achieve a homogeneous temperature distribution upon thesurface of the substrate, the filament of a heating element preferablyhas a centrally disposed, coiled section with adjoining uncoiledsections, whereas the filament of the adjacent heating element has acorresponding uncoiled central section and two adjacent coiled sections.As a result of this arrangement, a different heating-up of the edgeregions of the substrate relative to the central region is made possiblein order to counteract the aforementioned photon-box-effect. In thisconnection, the coiled central section of the one filament preferablyhas a length of approximately ⅘ of the diameter of the substrate that isto be treated. The coiled sections that are adjacent to a central,uncoiled section preferably have a length of approximately ⅓ of thediameter of the substrate that is to be treated.

[0018] For a good and uniform heating-up of the substrates, the heatingelements are preferably rod lamps, the filaments of which deviate fromthe longitudinal axis of the lamps by less than one millimeter.

[0019] The object of the invention is realized with an apparatus for thethermal treatment of substrates, especially disc-shaped semiconductorsubstrates, which apparatus has a housing that forms an oven chamber, atleast one radiation source within the oven chamber, and a processchamber for accommodating the substrate that is to be treated, wherebythe process chamber is essentially transparent for the radiation of theradiation source, and whereby the housing has inner walls that arereflective for the radiation, in that at least one inner wall of thehousing, which is disposed approximately parallel to a plane of thesubstrate that is to be treated, has at least two zones having differentreflection characteristics, whereby at least one zone essentiallycorresponds to the projected shape of the substrate. By providing thedifferent reflection characteristics, a local heating-up of the processchamber, which is caused by thermal radiation that is emitted from thesubstrate and that is partially absorbed by the process chamber andreflected at the inner walls of the housing, can be reduced. Due to thefact that one zone essentially corresponds to the projected shape of thesubstrate, a local heating-up of the process chamber directly above thesubstrate, especially in a region that essentially corresponds to theprojected shape of the substrate, can be reduced.

[0020] Preferably, the light incident in one zone is reflected in anessentially diffused manner, as a result of which a uniform distributionresults within the oven chamber of the thermal radiation that is emittedfrom the substrate and is reflected in the one zone. To achieve thiseffect, the zone of the inner wall is preferably blasted with sand orabrasive, or is roughened by some other chemical, electrochemical, ormechanical process.

[0021] Pursuant to one embodiment of the invention, the one inner wallhas a shape that is different from the projected shape of the substrate,for example having a quadratic shape in comparison to a round substrateshape. The one zone preferably corresponds essentially to the size ofthe substrate.

[0022] The object of the present invention is also realized with anapparatus for the thermal treatment of substrates, especiallydisc-shaped semiconductor substrates, which apparatus has a housing thatforms an oven chamber, at least one radiation source within the ovenchamber, and a process chamber for accommodating the substrate that isto be treated, wherein the process chamber is essentially transparentfor the radiation of the radiation source, in that at least one wall ofthe process chamber that is disposed essentially parallel to a plane ofthe substrate that is to be treated is provided with at least two zoneshaving different optical characteristics, whereby one zoneadvantageously essentially corresponds to the projected shape of thesubstrate. In this way, localized heating of the process chamber wallabove and below the substrate due to the thermal radiation given offfrom the substrate can be reduced, and hence an overheating of thecentral portion of the substrate can be counteracted.

[0023] Pursuant to one embodiment of the invention, the one zone isessentially transparent for the thermal radiation given off by thesubstrate in order in this manner to avoid a local heating-up especiallyin this region. In this connection, the one wall of the process chamberpreferably has a shape that is different from the projected shape of thesubstrate, and the one zone corresponds essentially to the size of thesubstrate.

[0024] The invention will be described subsequently in greater detailwith the aid of preferred embodiments with reference to the drawings;shown in the drawings are:

[0025]FIG. 1 a schematic cross-sectional view from the front through arapid heating unit;

[0026]FIG. 2 a schematic cross-sectional view from the side through arapid heating unit;

[0027]FIG. 3 a schematic cross-sectional view through a rapid heatingunit, whereby lamps pursuant to the present invention are shown in anupper bank of lamps;

[0028]FIG. 4 a schematic view of a lamp group pursuant to the presentinvention;

[0029]FIG. 5 a schematic cross-sectional view through a rapid heatingunit pursuant to the present invention having different segmented lampgroups in the upper and lower banks of lamps;

[0030]FIG. 6 a schematic illustration of different arrangementpossibilities of lamp groups in the upper and lower banks of lamps in arapid heating unit;

[0031]FIG. 7 a schematic plan view onto a schematic rapid heating unithaving an upper bank of lamps with segmented heating lamps;

[0032]FIG. 8 a view similar to FIG. 5, whereby the individual segmentsof the segmented lamps in the upper and lower banks of lamps havedifferent length ratios;

[0033]FIGS. 9a and 9 b schematic illustrations of heating filaments, ofheating lamps of one group of heating lamps, that are complementary insections;

[0034]FIG. 10 is a schematic plan view onto an oven chamber wall havingzones of different reflection characteristics.

[0035]FIG. 1 schematically shows the overall construction of a rapidheating unit 1 for semiconductor wafers 2. The rapid heating unit has anonly schematically indicated housing 4 (which can also be designated asa reactor) that internally defines an oven chamber 6. The inwardlyfacing walls of the housing can be coated at least partially in order toform a reflector chamber. Provided centrally within the oven chamber 6is a process chamber 8 that is comprised of transparent quartz glass.Within the process chamber 8, the wafer 2 that is to be treated isplaced upon appropriate support elements 9. The housing 4, as well asthe process chamber 8, each have non-illustrated, closable openings forthe introduction and removal of the wafers 2. Furthermore,non-illustrated gas lines are provided for conveying process gases intoand out of the process chamber 8.

[0036] Provided above and below the process chamber 8 are banks of lamps11,12, which are each formed by a plurality of rod-shaped tungstenhalogen lamps 14. Although this is not illustrated in FIG. 1, it is alsopossible to provide banks of lamps or individual tungsten halogen lamps14 to the sides of the process chamber 8. It is, of course, to beunderstood that in place of the rod-shaped tungsten halogen lamps, itwould also be possible to use other lamps.

[0037] The wafer that is disposed in the process chamber 8 is heated bythe electromagnetic radiation emitted from the banks of lamps 11,12. Apyrometer 16 is provided for measuring the wafer temperature.

[0038] With reference to FIG. 3, a special embodiment of a rapid heatingunit pursuant to the present invention will now be described, with thisembodiment in general having the same construction as does thepreviously described rapid heating unit. Therefore, the same or similarelements have the same reference numerals as used in conjunction withthe description of the rapid heating unit of FIGS. 1 and 2.

[0039] The rapid heating unit 1 has a housing 4, of which only an upperwall 18 and a lower wall 19 are illustrated. The housing 4 forms an ovenchamber 6 in which is disposed a process chamber 8 comprised of quartzglass. Disposed within the process chamber 8 is a semiconductor wafer 2that is surrounded by a compensation ring 20 that is disposed on theplane of the semiconductor wafer 2. Also indicated in FIG. 3 is a gasinlet or outlet opening 22 for conveying process gases into or out ofthe process chamber 8.

[0040] Provided above and below the process chamber 8 are banks of lamps11,12. Disposed in the lower bank of lamps 12 is a plurality ofconventional tungsten halogen lamps 14, only one of which is shown inFIG. 3.

[0041] In the upper bank of lamps 11, each two differently segmentedlamps 24,25 form a lamp group 26, which can also be designated as amultiple lamp. The lamp bulbs or tubes of the lamps 24,25 are secured tocommon lamp sockets 28,29. The lamp socket 28, as well as the lampsocket 29, each have a non-illustrated connection by means of which notonly the lower but also the upper lamps 24, 25 can be activated. Thelamps, with their common socket, can be dimensioned such that they canbe used in lamp-receiving means of existing rapid heating units, therebyenabling a retrofitting of existing systems. The connection is such thatthe upper and lower lamps can be activated separately from one another,in other words individually and independently of one another.Alternatively, it is, of course, also possible to provide for each ofthe lamps its own socket having its own connection.

[0042] The upper lamps 24 are provided with a heating wire or filament30 having a coiled central portion and uncoiled or at least much lesscoiled sections 34. The coiled section 32 is disposed entirely in theregion of the wafer 2. The uncoiled or much less coiled sections 34adjoin the coiled section 32 to the left and to the right, and overlapan edge region of the wafer 2.

[0043] The lamp 25 has an uncoiled or not very coiled central section36, and coiled edge sections 38. The uncoiled central section 36 of thelamp 25 extends over the same range as does the coiled central section32 of the lamp 24. In the same manner, the coiled edge sections 38 ofthe lamp 25 extend over the same region as do the uncoiled sections 34of the lamp 24.

[0044] The coiled and uncoiled sections of the lamps 24 and 25 are thuscomplementary to one another. As a result of different activation of thelamps 24 and 25, it is possible in a straightforward manner to achieve adifferent heating of the central portion of the substrate relative tothe edge portion thereof. During a heating-up phase, for example, thelamp 24 can be activated more pronounced than is the lamp 25, as aresult of which a higher irradiation intensity occurs in the centralportion of the wafer 2 relative to the edge portion thereof.Consequently, the photon-box-effect can be reduced during the heating-upphase. During the controlled cooling-off of the wafer 2, in other words,during the cooling-off accompanied by simultaneous irradiation via thelamps 24,25, the lamp 25 can now be activated more pronounced than isthe lamp 24, as a result of which a greater irradiation intensity occursin the edge portion of the wafer 2 than in the central portion thereof.This reduces a more rapid cooling-off of the edge region and hencereduces the photon-box-effect.

[0045] The filaments of the lamps have a constant electrical resistanceper unit of length of the filament over the entire filament length, sothat the coiled regions irradiate with the same intensity at the sameactivation. Alternatively, however, the filaments could also have adifferent electrical resistance per unit of filament length in order toachieve different irradiation intensities. In this way, a wideadaptation of the irradiation characteristics can be achieved.

[0046] Although this is not illustrated in FIG. 3, during the thermaltreatment the wafer 2 can be rotated in the plane of the wafer in orderto achieve an even more uniform temperature distribution over thesurface of the wafer.

[0047]FIG. 4 schematically shows an embodiment of an inventive lampgroup 40 which can be used, for example, in place of the lamp group 26shown in FIG. 3. The lamp group 40 has an upper lamp 42 as well as alower lamp 43, which are respectively secured at their respective endsto a common socket 44, 45. The heating wire or filament 47 of the upperlamp has an uncoiled central section 48, as well as respective coilededge sections 49 adjoining the central section. The upper lamp 42 has alamp tube 50 that is comprised of quartz glass and that, via partitions51 that extend transverse to the longitudinal axis of the lamp, formsthree chambers 55, 56, 57 that are separated from one another. Thelength of the chambers 55 and 57 centrally corresponds to the length ofthe coiled edge sections 49 and accommodates the same. The middlechamber 56 has a length that essentially corresponds to the length ofthe central, uncoiled section 48 of the filament 47 and accommodates thesame.

[0048] A different gas atmosphere (gas composition and/or pressure) isfound in the chambers 55 and 57 than in the chamber 56. If the filament47 of the upper lamp is activated, this filament, due to the coiled edgeregions 49, is heated more pronounced in the coiled edge sections 49than in the uncoiled central section 48. In order nonetheless to providea stable halogen process over the entire length of the lamp, there isprovided in the middle chamber 56 a gas atmosphere that enhances ahalogen process even at low temperatures. The gas atmospheres in therespective chambers are adapted to the expected heating of therespective filament sections.

[0049] The lower lamp 43 is provided with a heating wire or filament 67having a coiled central section 68 and uncoiled edge sections 69 thatare complementarily disposed relative to the coiled and uncoiledsections 49, 48 of the lamp 42. In the same manner as the lamp 42, thelamp 43 has a lamp tube 70 that is divided into different chambers 75,76, 77 via partitions 71 that extend transverse to the longitudinal axisof the lamp. The outer chambers 75 and 77 accommodate the uncoiledsections 69 of the filament 67, while the middle chamber 76 accommodatesthe coiled section 68 of the filament 67. The chambers 75 and 77 againhave a different gas atmosphere than does the chamber 76.

[0050] The separation of the chambers can be effected, for example, bymetal, glass or ceramic partitions that are sealed into the lamp tube.Alternatively, however, a tapering of the lamp tube can also effect aseparation of the chambers without additional elements.

[0051]FIG. 5 shows an alternative embodiment of a rapid heating unit 1that is essentially constructed the same as the rapid heating unit 1 ofFIG. 3. In contrast to the embodiment of FIG. 3, with the embodiment ofFIG. 5 also for the lower bank of lamps 12 each two lamps form a grouphaving complementarily arranged coiled and uncoiled sections. Thus,provided above and below a substrate 2 are banks of lamps 11, 12 thatare provided with complementarily segmented and grouped lamps.

[0052]FIG. 6 illustrates different possibilities for arranging thegroups that comprise two complementarily segmented lamps. With regard tothe lamp groups, the circle that contains the cross respectivelyrepresents a lamp having a centrally coiled section and uncoiled or lessgreatly coiled edge sections, whereas the circle having the filled-inpoint represents a lamp having a non-coiled or slightly coiled centralsection and coiled or more greatly coiled edge sections. The examples Iand II represent the presently preferred embodiment of the invention,according to which the respective lamps of a lamp group are disposed ona line that is perpendicular to the plane of the wafer.

[0053] However, as illustrated in example III, it is also possible todispose the respective lamps of a lamp group in a plane that extendsparallel to the plane of the wafer.

[0054] The examples IV and V show an arrangement of the respective lampsin a plane that intersects the wafer at an angle of other than 90degrees. With the examples I, II, III and V, the respective lamps of thelamp groups of the upper and lower bank of lamps are disposedsymmetrically relatively to the plane of the wafer.

[0055] In contrast, example VI shows an arrangement of the lamps of thelamp group of the upper bank of lamps in a plane that intersects theplane of the wafer at an angle other than 90 degrees, whereas the lampsof a lamp group of the lower bank of lamps are disposed parallel to theplane of the wafer.

[0056] There thus results different possibilities for arranging thelamps within the respective lamp groups.

[0057]FIG. 7 shows a schematic plan view onto a rapid heating unit 1,whereby the upper wall of the oven chamber has been removed. The ovenchamber is provided with end walls 80 and 81, as well as with chamberside walls 82 and 83 that connect the chamber end walls 80, 81. Thechamber end wall 80 is provided with an opening for receiving andguiding a gas line 89 through that is in communication with a processchamber 88 that is disposed in the interior of the oven chamber.

[0058] Extending between the chamber side walls 82, 83, in at least twoplanes, are lamp pairs 90 a to q (of which only the upper lamps areillustrated, and which can be disposed, for example, analogously orsimilarly to the lamp pairs in the bank of lamps 11 in FIG. 3) of anupper bank of lamps 91, which will be explained in greater detailsubsequently. A further bank of lamps can be provided below the processchamber 88, although this is not illustrated in FIG. 7. Provided on thechamber end wall 81 is an adapter 95 for a gas discharge system. The gasdischarge system in the adapter 95 is designed such that it enables alaminar gas flow within the process chamber 8. There is furthermoreprovided on the chamber end wall 81 a door for loading and unloading theprocess chamber 88.

[0059] Provided in the non-illustrated base and/or in thenon-illustrated top wall of the oven chamber is a plurality of gasinlets that are directed toward the process chamber 8 in order to coolthe process chamber by the introduction of a gas.

[0060] A semiconductor wafer 97 is accommodated within the processchamber 88 and is radially surrounded by a compensation ring 98. Thewafer is accommodated in such a way that it is rotatable about itscentral axis in the plane of the wafer.

[0061] As is illustrated in FIG. 7, the upper plane of the upper bank oflamps 91 is provided not only with segmented lamps, i.e. lamps havingcoiled and uncoiled or less greatly coiled sections of the filament, butalso non-segmented lamps, i.e. lamps having a generally essentiallyuniformly coiled filament. In the segmented lamps, i.e. the lamps 90 a,b, c, d, e, g, k, l, m, n, o, q, the respective central sections of thefilaments are uncoiled or at least not greatly coiled, whereas therespective end sections are coiled. In the second plane of the upperbank of lamps 91, the lamps are inventively embodied to be complimentaryto the corresponding upper lamps. In this way, essentially strip-shapedzones A and B result having different radiation intensities that areemitted from the lamps. In the central zone A there is effected aradiation essentially only via the generally uniformly coiled lamps 90f, i, j, k, and p, and via the lamps of the second plane of the upperbank of lamps that are coiled in the central region. In the edge zonesB, the irradiation is effected essentially by the lamps that in the edgeregion include a coiled filament. Overall, the generally uniformlycoiled lamps (lamp pairs) 90 f, i, j, k, and p can also be replaced bypairs of complementarily segmented lamps. From the arrangement and theratio of the number of complimentarily segmented pairs and generallycoiled lamps, as well as their electrical activation, the zones A and Bcan be defined and their magnitude and intensity of irradiation can becontrolled during the process.

[0062] As a result of this arrangement of the lamps in combination withthe rotation of the wafer there result upon the surface of the wafer 97two different irradiation zones, which are illustrated in FIG. 7 by thedotted line. Within the dotted line, i.e. in a central portion of thewafer, there is effected an irradiation essentially exclusively via thenon-segmented lamps whereas in the region of the wafer disposed beyondthe dotted circle, an irradiation is effected not only by thenon-segmented but also by the segmented lamps, in particular thesegmented lamps 90 g, 90 k and 90 l. By means of suitable individualactivation of the respective lamps it is therefore possible to heat thecentral portion of the wafer 97 differently (and in particular as afunction of the process) from its edge region.

[0063] Such a multi-zone irradiation can also be achieved by the use ofthe lamp groups illustrated in FIGS. 3, 4, 5 and 6, whereby thearrangement of the lamp pairs or groups and/or of their combinationswith non-segmented lamps can be combined in any desired fashiondepending upon requirements. Thus, for example, the lamp pairs describedin conjunction with FIG. 7 can be replaced by other groupings, such asthose illustrated in FIG. 6. Furthermore, different groupings are alsopossible within a bank of lamps.

[0064]FIG. 8 shows a schematic cross-sectional view of a furtherembodiment of a rapid heating unit 1 pursuant to the present invention,which has a similar construction to the rapid heating unit 1 of FIG. 5.The single difference lies in a different ratio of the lengths of thecoiled and uncoiled sections in the lamp groups of the upper bank oflamps 11 and the lamp groups of the lower bank of lamps 12. Theillustrated sectional lengths are provided in millimeters and areprovided for a rapid heating unit for wafers 2 having a diameter of 200mm. For the lamp group of the upper bank of lamps 11 the length of thecentral section is 140 mm, whereas the edge sections respectively have alength of 80 mm. For the lamp group of the lower bank of lamps 12 thecentral section has a length of 160 mm, whereas the edge sectionsrespectively have a length of 70 mm. Due to the different ratios of thesectional lengths there result different zones having differentirradiation intensities, which enables an improved heating of the wafer2 and a reduction of the photon-box-effect. The indicated lengths of thesections are provided only as examples and are not limiting. Thesectional lengths can be adapted to the respective wafer size and thechamber geometry.

[0065]FIGS. 9a and b show two different embodiments of lamp groups eachhaving two lamps with a lamp filament that is respectively provided withcoiled and uncoiled sections. As can be seen in FIGS. 9a and b, thecoiled and uncoiled sections of the two lamps of a lamp group are,however, only partially complementary. Thus, pursuant to FIG. 9a, forexample, with both lamps of the lamp group an edge region havinguncoiled sections of the respective filament are provided. Furthermore,the coiled central section of the lower lamp does not entirely overlapthe uncoiled central section of the upper lamp. At the same time, thecoiled central section of the lower lamp slightly overlaps the rightcoiled section of the upper lamp.

[0066] Due to the different arrangement of the coiled and uncoiledregions, different irradiation profiles of the lamp groups can beprovided that can be adapted to the respective processes and the chambergeometries.

[0067] Pursuant to one possible overlapping of coiled or non-coiledsections of adjacent lamps of a lamp group, this overlapping should beless than 30% of the section length or 10% of the substrate diameter.

[0068]FIG. 10 shows a schematic illustration of an upper or lower ovenchamber wall of a rapid heating unit 1, which wall is disposed parallelto the plane of the wafer. FIG. 10 shows the inner chamber wall, which,as described previously, can be reflective or coated. The reflectivecharacter is effected, for example, by a coating with gold or adielectric material. In this connection, the inner side of the oven wallhas, however, a central region 100 that has a shape that corresponds tothe projected shape of the wafer that is to be treated. In theillustrated embodiment, a circular shape is provided. Notches or flatsprovided on the wafer are not necessarily taken into consideration forthe design of the central region 100.

[0069] The central region 100 is surrounded by an outer region 102. Theregions 100 and 102 are provided with different reflectivecharacteristics. In particular, the central region 100 reflects incidentlight in a diffused manner and/or has a lower reflection coefficientthan does the outer region. There is preferably reflected in the outerregion 102 a normal (specular) reflection. In general, the regions canalso differ in the spectral nature of their optical characteristics,e.g. in the spectral nature of the refraction index and/or in thereflection coefficients, whereby, for example, a reflection coefficientintegrated over a specific wave length range can be continuously uniformor similar. The central region 100 can, for example, be treated bysandblasting or streams of abrasive in order to obtain the diffusedreflection characteristics. The spectral nature of the opticalcharacteristics can be influenced, for example, via different coatingsof the central and outer regions.

[0070] The size of the central region 100 essentially corresponds to thesize of the substrate that is to be treated, whereby this is again afunction of the dimensions of the process chamber or reactor. If thereflecting and/or refracting surfaces are at a distance of less than 30%from the surface of the wafer, the central region is between 70% and130% of the wafer diameter. Included in the selection of the suitablediameter are the optical characteristics of the wafer, the arrangementof the banks of lamps, and the temperature-time curves of the intendedprocess. One tries to undertake a selection that is largely independentof the first and last, whereby the parameters for the central region arethen as indicated. It can furthermore be advantageous to provide morethan two regions with different optical characteristics and/or tocontinuously vary the optical characteristics, so that, for example, thereflection coefficient of the outer region continuously increases ordecreases toward the outside.

[0071] Inner oven walls having regions of different reflectivity lead,during longer processes, to a more homogeneous distribution of thetemperature over the surface of the wafer. Even during short, so-calledflash processes, an improved homogeneity of the distribution of thetemperature of the wafer can be achieved. Furthermore, with units havingsuch modified chamber surfaces, the banks of lamps having conventionalnon-segmented lamps, all of the lamps of a bank of lamps can beactivated with nearly the same electrical power. Up to now, the lampswere differently activated to reduce edge effects. The uniformactivation leads to an increase of the service life of the lamps. Inaddition, with the same electronic power mechanisms, a larger processwindow or a larger control or regulation region is achieved, since allof the lamps can be activated essentially identically. In this way,situations are avoided where a lamp having 40% power is irradiating,while another lamp is irradiating with 80% power, as a result of which amaximum increase of the irradiation capacity, with the irradiationconditions between the lamps remaining the same, results. With a uniformactivation of the lamps, the regulation regions of the lamps can bebetter utilized. This increases the process dynamic and the regulationregion. In this connection, none of the lamps should significantlydiffer upwardly or downwardly from an average value, i.e. the lampcapacities are disposed approximately within a capacity or power windowof about 20% about the average value. A further increase of the processwindow can be achieved by a lower loading of the lamps, if utilized,that are mounted on the side inner walls of the oven. Instead of aloading of nearly 100%, as is normally customary for these lamps, theside lamps are loaded, for example, only to 30% for processes in an oventhat has regions of different reflectivity. If in addition to the ovenregions that are prepared by sandblasting or streams of abrasive, thebanks of lamps are equipped with the inventive lamp groups or multiplelamps, it is possible to still further increase the homogeneity of thetemperature with their help if the irradiation characteristics of theindividual heating bodies, and thus the irradiation field within theoven chamber, are adapted by zones to the process requirements.

[0072] In a similar manner, the chamber walls of the process chamber,which is comprised of quartz, and which chamber walls are disposedparallel to the plane of the wafer, can also be provided with regionshaving different optical characteristics, whereby one region has aprojected shape in conformity with the wafer that is to be treated. Thedifferent optical characteristics can, for example, include a differentrefraction, especially of the thermal radiation emanating from thewafer, and/or a different absorption magnitude of the thermal radiationemanating from the wafer. In this way, there is avoided that the chamberwall that is disposed parallel to the wafer is locally heated up more inthe region above or below the wafer than are other regions of theprocess chamber, which would reinforce the previously describedphoton-box-effect.

[0073] The invention was previously described in detail with the aid ofpreferred embodiments of the invention without being limited to thespecifically illustrated embodiments. The heating unit can, for example,be utilized for RTP-, CVD-, RTCVD-, or epitaxial processes. Thepreviously mentioned features can be combined with one another in anycompatible manner. In particular, the chamber wall having differentreflectivities, or the process chamber wall having different opticalcharacteristics, can be combined with the various lamp forms.

1. Apparatus (1) for the thermal treatment of substrates (2), especiallysemiconductor wafers, including at least two adjacent heating elements(24, 25; 42,43; 90 a-q) that are disposed essentially parallel to oneanother and are each provided with at least one heating filament,characterized in that the at least two adjacent heating elements (24,25; 42, 43; 90 a-q), at least in part, are embodied approximatelycomplementary to one another with respect to coiled (32,38; 49,68) anduncoiled (34, 36; 48, 69) sections of their heating filaments. 2.Apparatus (1) according to claim 1, characterized in that the filamentof the one heating element (24, 25; 42, 43; 90 a-q) has n coiledsections (32, 38; 49, 68) and m uncoiled sections (38, 36; 48, 69),while the filament of the adjacent heating element has m coiled and nuncoiled sections, whereby m and n are respectively natural numbers. 3.Apparatus (1) according to claim 2, characterized in that the coiledsections (32, 38; 49, 68) of the filament of one heating element (24,25; 42, 43; 90 a-q) are respectively disposed at least partially in theregion of the uncoiled sections (34, 36; 48, 69) of the filament of theadjacent heating element.
 4. Apparatus (1) according to claim 3,characterized in that the coiled (32, 38; 49, 68) or uncoiled sections(34, 36; 48, 69) of filaments overlap by at most 10% of the diameter ofthe substrate (2) that is to be treated.
 5. Apparatus (1) according toone of the preceding claims, characterized in that the filaments aresymmetrical relative to a plane of symmetry that centrally intersectsthe longitudinal axis of the filaments and is disposed perpendicularthereto.
 6. Apparatus (1) according to one of the preceding claims,characterized in that respectively at least two adjacent heatingelements (24, 25; 42, 43; 90 a-q) form a group (26; 40), the heatingelements (24, 25; 42, 43; 90 a-q) of which are associated with oneanother on at least one side.
 7. Apparatus (1) according to claim 8,characterized in that the heating elements (24, 25; 42, 43; 90 a-q) of agroup (26; 40) have a common socket (28, 29; 44, 45).
 8. Apparatus (1)according to one of the preceding claims, characterized by a controldevice for the individual activation of the filaments of adjacentheating elements (24, 25; 42, 43; 90 a-q).
 9. Apparatus (1) according toone of the preceding claims, characterized in that the respectivefilaments have a constant electrical resistance per unit of length. 10.Apparatus (1) according to one of the preceding claims, characterized inthat at least one heating element (42; 43) has at least two chambers(55, 56, 57; 75, 76, 77) for accommodating the filament.
 11. Apparatus(1) according to one of the preceding claims, characterized in that theheating elements (42; 43) have a plurality of chambers (55, 56, 57; 75,76, 77) that are separated from one another and serve for receivingdifferent sections of the filaments.
 12. Apparatus according to claim 10or 11, characterized in that a different pressure and/or a different gasis provided in at least two of the chambers (55, 56, 57; 75, 76, 77).13. Apparatus (1) according to one of the preceding claims,characterized in that the filament of one heating element (24; 43) has acentrally disposed coiled section (32; 68) with adjoining uncoiledsections (34; 69) whereby the filament of the adjacent heating element(25; 42) has a corresponding uncoiled central section (36; 48) with twoadjacent coiled sections (38; 49).
 14. Apparatus (1) according to claim13, characterized in that the coiled section (32; 68) of the onefilament has a length of approximately ⅘ of the diameter of thesubstrate (2) that is to be treated.
 15. Apparatus (1) according toclaim 13 or 14, characterized in that the coiled sections that aredisposed adjacent to a central, uncoiled section have a length ofapproximately ⅓ of the diameter of the substrate that is to be treated.16. Apparatus according to one of the preceding claims, characterized inthat the heating elements (24, 25; 42, 43; 90 a-q) are rod lamps, thefilaments of which deviate from the longitudinal axes of the lamps byless than 1 mm.
 17. Apparatus according to one of the preceding claims,characterized by an oven chamber that surrounds the heating elements andthat, for an irradiation of the heating elements, is provided withreflective inner walls, whereby one inner wall that is disposedapproximately parallel to a plane of the substrate that is to be heatedis provided with at least two zones having different reflectioncharacteristics, and whereby at least one zone corresponds essentiallyto the projected shape of the substrate.
 18. Apparatus according toclaim 17, characterized in that the one zone reflects light that isincident therein in an essentially diffused manner.
 19. Apparatusaccording to claim 17 or 18, characterized in that the one zone of theinner wall is blasted with sand or abrasive.
 20. Apparatus according toone of the claims 17 to 19, characterized in that one other zone has ashape that differs from the projected shape of the substrate. 21.Apparatus according to one of the claims 17 to 20, characterized in thatthe one zone corresponds essentially to the size of the substrate. 22.Apparatus according to one of the preceding claims, characterized by aprocess chamber for accommodating the substrate that is to be treated,whereby the walls of the process chamber are disposed between theheating elements and the substrates and are essentially transparent fora radiation of the heating elements, whereby a wall of the processchamber that is disposed essentially parallel to a plane of thesubstrate that is to be treated is provided with at least two zoneshaving different optical characteristics, and whereby one zonecorresponds essentially to the projected shape of the substrate. 23.Apparatus according to claim 22, characterized in that the one zone isessentially transparent for thermal radiation emitted from thesubstrate.
 24. Apparatus according to one of the claims 22 or 23,characterized in that the one wall of the process chamber has a shapethat differs from the projected shape of the substrate.
 25. Apparatusaccording to one of the claims 22 to 24, characterized in that the onezone corresponds essentially to the size of the substrate.
 26. Apparatusfor the treatment of substrates, especially disk-shaped semiconductorsubstrates, including a housing that forms an oven chamber, at least onesource of radiation within the oven chamber, and a process chamber foraccommodating the substrate that is to be treated and that isessentially transparent for the radiation of the source of radiation,characterized in that at least one wall of the process chamber that isdisposed essentially parallel to a plane of the substrate that is to betreated is provided with at least two zones having different opticalcharacteristics, whereby one zone corresponds essentially to theprojected shape of the substrate.
 27. Apparatus according to claim 26,characterized in that the one zone is essentially transparent forthermal radiation emitted from the substrate.
 28. Apparatus according toone of the claims 26 or 27, characterized in that the one wall of theprocess chamber has a shape that differs from the projected shape of thesubstrate.
 29. Apparatus according to one of the claims 26 to 28,characterized in that the one zone corresponds essentially to the sizeof the substrate.
 30. An apparatus for thermally treating substrates,comprising: at least two adjacent heating elements 24, 25; 42, 43; 90a-q that extend essentially parallel to one another and are eachprovided with at least one heating filament, each of which includescoiled 32, 38; 49, 68 and uncoiled 34, 36; 48, 69 sections, wherein atleast parts of said at least two adjacent heating elements are embodiedapproximately complementary to one another with respect to said coiledand uncoiled sections of pertaining ones of said filaments.
 31. Anapparatus according to claim 30, wherein said filament of one of saidheating elements has n coiled sections 32, 38; 49, 68 and m uncoiledsections 34, 36; 48, 69, while the filament of an adjacent heatingelement has m coiled sections and n uncoiled sections, where m and n arerespectively integers.
 32. An apparatus according to claim 31, whereinsaid coiled sections 32, 38; 49, 68, of said filament of one of saidheating elements are respectively disposed at least partially in aregion of said uncoiled sections 34, 36; 48, 69 of said filament of theadjacent heating element.
 33. An apparatus according to claim 32,wherein said coiled or uncoiled sections of said filaments overlap by atmost 10% of a diameter of a substrate that is to be treated.
 34. Anapparatus according to claim 30, wherein said filaments are symmetricalrelative to a plane of symmetry that centrally intersects longitudinalaxes of said filaments and is disposed perpendicular thereto.
 35. Anapparatus according to claim 30, wherein respectively at least twoadjacent ones of said heating elements form a group 26, 40, the heatingelements of which on at least one side are associated with one another.36. An apparatus according to claim 35, wherein the heating elements ofa group 26, 40 have a common socket 28, 29; 44,
 45. 37. An apparatusaccording to claim 30, wherein a control device is provided for anindividual activation of said filaments of adjacent ones of said heatingelements.
 38. An apparatus according to claim 30, wherein said filamentsrespectively have a constant electrical resistance per unit of length.39. An apparatus according to claim 30, wherein at least one of saidheating elements 42, 43 has at least two chambers 55-57; 75-77 foraccommodating said filament thereof.
 40. An apparatus according to claim39, wherein said heating elements 42, 43 have a plurality of chambers55-57; 75-77 that are separated from one another and serve for receivingdifferent sections of said filaments.
 41. An apparatus according toclaim 39, wherein at least one of a different pressure and a differentgas is provided in at least two of said chambers 55-57; 75-77.
 42. Anapparatus according to claim 30, wherein said filament of one of saidheating elements 24, 43 has a centrally disposed coiled section 32, 68with adjoining uncoiled sections 34, 69, and wherein said filament of anadjacent one of said heating elements 25, 42 has a correspondinguncoiled central section 36, 48 with two adjoining coiled sections 38,49.
 43. An apparatus according to claim 42, wherein said coiled centralsection 32, 38 of said one filament has a length of approximately ⅘ of adiameter of a substrate that is to be treated.
 44. An apparatusaccording to claim 42, wherein said coiled sections that are disposedadjacent to a central, uncoiled section have a length of approximately ⅓of a diameter of a substrate that is to be treated.
 45. An apparatusaccording to claim 30, wherein said heating elements are rod-lamps, thefilaments of which deviate from longitudinal axes of said lamps by lessthan 1 mm.
 46. An apparatus according to claim 30, wherein an ovenchamber is provided that surrounds said heating elements and isprovided, for a radiation of said heating elements, with reflectiveinner walls, wherein one inner wall that is disposed approximatelyparallel to a plane of a substrate that is to be treated is providedwith at least two zones having different reflection characteristics, andwherein at least one of said zones corresponds essentially to aprojected shape of said substrate.
 47. An apparatus according to claim46, wherein said at least one zone reflects light that is incidenttherein in an essentially diffused manner.
 48. An apparatus according toclaim 46, wherein at least one zone of said inner wall is blasted withabrasive.
 49. An apparatus according to claim 46, wherein one other zonehas a shape that differs from said projected shape of said substrate.50. An apparatus according to claim 46, wherein said at least one zonecorresponds essentially to a size of said substrate.
 51. An apparatusaccording to claim 30, wherein a process chamber is provided foraccommodating a substrate that is to be treated, wherein said processchamber has walls that are disposed between said heating elements andsaid substrate and that are essentially transparent for a radiation ofsaid heating elements, wherein a wall of said process chamber that isdisposed essentially parallel to a plane of a substrate that is to betreated is provided with at least two zones having different opticalcharacteristics, and wherein one of said zones corresponds essentiallyto a projected shape of said substrate.
 52. An apparatus according toclaim 51, wherein said one zone is essentially transparent for thermalradiation emitted from said substrate.
 53. An apparatus according toclaim 51, wherein said one wall of said process chamber has a shape thatdiffers from said projected shape of said substrate.
 54. An apparatusaccording to claim 51, wherein said one zone corresponds essentially toa size of said substrate.
 55. An apparatus for thermally treatingsubstrates, comprising: a housing 4 that forms an oven chamber 6; atleast one source of radiation disposed within said oven chamber 6; and aprocess chamber 8 disposed in said housing 4 for accommodating asubstrate that is to be treated, wherein said process chamber 8 isessentially transparent for radiation of said source of radiation,wherein at least one wall of said process chamber 8 that is disposedessentially parallel to a plane of said substrate that is to be treatedis provided with at least two zones having different optical properties,and wherein one of said zones essentially corresponds to a projectedshape of said substrate.
 56. An apparatus according to claim 55, whereinsaid one zone is essentially transparent for thermal radiation emittedfrom said substrate.
 57. An apparatus according to claim 55, whereinsaid one wall of said process chamber has a shape that differs from saidprojected shape of said substrate.
 58. An apparatus according to claim55, wherein said one zone corresponds essentially to a size of saidsubstrate.